Although databases are used for various uses, the use of a relational database (RDB) which can eliminate a logical contradiction has become the mainstream in a medium-scale to large-scale system. For example, the RDB is used in a system of an airline seat reservation or the like. In this case, by specifying a key item, it is possible to quickly retrieve targets (one target in many cases), or to confirm, cancel or change reservations. Besides, since the number of seats on each flight is several hundred at most, it is also possible to obtain the number of empty seats on a specific airline flight.
However, it is known that when an attempt is made to use this RDB to perform a specific operation (for example, calculation of the load factor) for each fiscal year, each day of the week, each month, each route, each time zone or each type of airplane, it takes a very long time. That is, while the RDB is superior in realizing a processing without contradictions, it has poor performance in searching, tabulating or sorting a considerable number of records.
Thus, in recent years, for the purpose of searching and tabulating, it has become general to construct a database called a data warehouse (DWH) in a system in addition to the RDB. That is, an extremely large-scale database having specific data formats and data item names to match the specific purpose of the end user is constructed, and the end user can use this to perform specific searches and tabulation.
However, to provide the DWH in addition to the RDB, that is, to provide plural databases deviates from the original form that the database, especially the RDB, was contrived for the purpose of enabling the central control of data, and this causes various problems as described below.    (1) Since the DWH is static, it is difficult to perform searching and tabulation of items other than those previously provided in the DWH.    (2) Since the static DWH is provided in addition to the RDB, the data capacity becomes extremely large, and it cannot deal with the update of the RDB and the like.
In view of the above problems, the present inventor invented a method of realizing a high speed join and filed this (PCT/WO00/73939). Also in this method, it is desirable that a data area necessary at an operation can be further reduced. Also in the above method of the join, there is a problem that a relatively large memory space is required since an array is created which becomes a product set of part of table-format data to be joined.
The present invention has an object to provide a structure of table-format data in which plural table-format data can be joined at desired high speeds and its data capacity is small, a concatenating method thereof, and a method of presenting the concatenated table-format data at extremely high speeds.
Besides, the invention has an object to provide a method in which at the time of a join processing, a large amount of data areas are not required for that.